JPH04303584A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To enhance resistance to dirt in a spark plug used in a supercharger or an internal combustion engine set to a high compression ratio by preventing a worn central electrode from causing jumping between the central electrode and a main metal fixture CONSTITUTION:The side periphery of a insulating body leg 14 is provided with a recess fitting part 10, in which an electrode 11 is installed by printing or applying paste-like ink mixed with a metal powder of 30-95wt.% and a ceramic powder of 70-5wt.%. From this electrode part 11 to main metal fixture 7, a lead part 12 is drawn out to carry current. In order to avoid penetrations between the electrode 11 and a central electrode 4, the electrode 11 is covered with an alumina green sheet 13, which is simultaneously baked with and closely bonded to the electrode 11. This can prevent jumping and, at the same time, adhesion and deposit of carbon on insulating body leg 14, and enhance resistance to smoking and dirt.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of an insulator leg portion of a spark plug used in an internal combustion engine, particularly an internal combustion engine with a high compression ratio setting or a supercharger.

0002

[Prior Art] In recent years, in order to achieve high output and low fuel consumption, modern internal combustion engines have been equipped with a high compression ratio in the combustion chamber, a turbocharger, etc. Equipped with a supercharger.

0003

[Problems to be Solved by the Invention] However, in the above-mentioned conventional engines, in order to achieve high output and low fuel consumption at the same time, it is necessary to set the compression ratio of the internal combustion engine at a high compression ratio, or to use a turbocharger. When equipped with a supercharger such as the above, the discharge voltage of the spark plug will increase due to high compression ratio settings.

When a spark plug is used for a long period of time, the center electrode of the spark plug tends to wear out severely, and if a high discharge voltage is continued to be applied while the center electrode is worn out, the contact between the center electrode and the outer electrode will deteriorate. Since the spark gap is large, it becomes difficult for ignition to occur between the center electrode and the outer electrode, causing a discharge phenomenon that leaks along the insulator surface to the metal shell, resulting in misfires, etc. There is.

[0005] Therefore, in order to prevent this jumping from the insulator surface to the metal shell, the initial setting of the spark gap between the center electrode and the outer electrode is made small to counteract the wear of the center electrode due to this spark discharge. However, in the initial setting of this spark gap, reducing the spark gap may sacrifice the ignitability of the air-fuel mixture at the beginning of use of the spark plug in an internal combustion engine equipped with a high compression ratio setting or a supercharger. I will do it.

[0006] Therefore, the present invention aims to improve the above-mentioned drawbacks of the conventional spark plugs, which are used in internal combustion engines equipped with high compression settings or superchargers, and which are subject to high discharge voltage. This makes it possible to prevent jumping caused by spark consumption.

[0007]

[Means for Solving the Problems] To this end, a concave portion is provided around the side circumference of the insulator long leg portion that holds the center electrode, and 30 to 95 wt% of metal powder and 70 to 5 wt% of ceramic powder are contained in this concave portion. An electrode part is formed by printing or coating a paste-like ink prepared in advance on an alumina green sheet or directly on the surface of an insulator, and the conduction of electricity from this electrode part to the metal shell is ensured. When the lead portion is drawn out and printed or coated directly on the surface of the insulator, the electrode portion is covered with an alumina green sheet and bonded closely by co-firing.

[0008] Furthermore, the position of the recess provided around the long leg portion of the insulator is such that the distance A from the front end face of the insulator is 2.0 mm or more, and the depth T of the recess is 0.1 mm or more. It is.

[0009]

[Operation] With the above structure, a recess is provided around the side of the insulator that holds the center electrode, and metal powder is placed in advance on an alumina green sheet or on the surface of the recess within the recess. By disposing an electrode part formed by printing or coating with a paste ink containing 30 to 95 wt% and 70 to 5 wt% of ceramic powder,
Since the electric field intensity distribution generated between the center electrode of the spark plug and the metal shell is weakened, jumping between the long leg portion of the insulator and the metal shell can be prevented.

Furthermore, carbon generated during low-temperature combustion is
Since it is electrically charged, the electric field strength distribution generated between the center electrode and the metal shell weakens,
It is possible to minimize the adhesion and accumulation of carbon, etc. on the tips of the long insulator legs, improving stain resistance and making it suitable for internal combustion engines equipped with turbochargers that use rich air-fuel mixtures. Even in use, it is possible to suppress the occurrence of misfire or pre-ignition.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further explained with reference to embodiments shown in the drawings. (1) is a spark plug for an internal combustion engine which is an embodiment of the present invention;
) holds the center electrode (4) at the tip of the shaft hole (3), and also holds one end of the resistor (5) and terminal electrode (6) sandwiched between the conductive glass seals (16) in the shaft hole (3). 3
) and an outer electrode (9) at a position opposite to the tip of a center electrode (4) held at the tip of the shaft hole (3) of the insulator (2), It is composed of a metal shell (7) having a threaded portion (8) on its side periphery that is screwed into the main body when it is mounted on an internal combustion engine.

In the embodiment shown in FIG. 2, the long leg portion (14) of the insulator (2) holding the center electrode (4)
A recessed portion (10) is provided around the side periphery of the
A paste ink containing 30 to 95 wt% of metal powder and 70 to 5 wt% of ceramic powder is printed or coated on the surface of the insulator (2) of the concave part (10) in this concave part (10). An insulator (2
), the electrode part (11) formed in the concave part (10) on the side circumference of the long leg part (14) of The thickness is 0.2-2.0 mm, preferably 0.0 mm, so that no penetration occurs between
．． Alumina green sheet with a thickness of 3 mm or more (13
) is coated with the electrode portion (11) and bonded to the electrode portion (11) by simultaneous firing.

[0013] Also, the electrode part (11) has a concave part (10).
Instead of printing or coating directly on the surface of the insulator (2) inside, an alumina green sheet (13
), the electrode part (11) can be formed by printing and applying a paste ink having the above composition, and this can also be printed and fitted into the recessed part (10) with the applied part inside, and then fired at the same time. (Figure 3). In this case, the electrode section (11
) can be formed and bonded to fit into the recessed fitting part (10), and furthermore, it is not necessary to cover this with another green sheet, so the work is easy.

[0014] The position of the concave portion (10) provided around the side circumference of the long leg portion (14) of the insulator (2) is similar to that of the center electrode (4).
The front end surface (1) of the long leg portion (14) of the insulator (2) projects
5), where A is the distance from If T, T≧0
．． It becomes 1mm.

[0015] Here, the position of the recessed part (10) provided around the side periphery of the long leg part (14) of the insulator (2) is determined from the center electrode (4).
) of the long leg portion (14) of the insulator (2) protrudes from the front end surface (
15) When the distance from the center electrode (4) is A, A≧2.0 mm is set because if the distance is not at least 2.0 mm, flashover and misfire will easily occur between the center electrode (4) and the tip. Therefore, 3.0 mm or more is preferable.

Furthermore, the long leg portion (14) of this insulator (2)
When T is the depth of the recessed part (10) provided around the side circumference of the recessed part (10), T≧0.1mm is satisfied.
Even if the green sheet (13) that covers and closely joins the electrode part (11) disposed inside shrinks due to simultaneous firing,
This is intended to prevent the insulator (2) from protruding from the surface of the long leg portion (4), thereby suppressing the occurrence of flashover.

[0017] Since the present invention has the above-described configuration, the central electrode (4) is disposed in the recess (10) provided around the side of the long leg portion (14) of the insulator (2) that holds the center electrode (4). , covered with alumina green sheet, adhered and bonded, metal powder 30~95wt%, ceramic powder 70~
The electrode part (11) is formed by printing or coating with a paste ink containing 5 wt%, or the electrode part (11) is formed by printing or coating on the green sheet.
1), the spark plug (1) installed in the internal combustion engine
) The electric field strength distribution generated between the center electrode (4) and the metal shell (7) is weakened, so that jumping can be prevented.

Furthermore, carbon generated during low-temperature combustion is
Since it is electrically charged, this center electrode (4) and the metal shell (7)
) By weakening the electric field strength distribution generated between It is possible to improve the resistance to fouling due to accumulation, and to suppress the occurrence of misfire or pre-ignition even when used in an internal combustion engine equipped with a supercharger that uses a rich air-fuel mixture.

Therefore, when comparing the embodiment of the present invention with the conventional structure in terms of the discharge voltage at which jumping occurs when a high voltage is applied as a load, as shown in FIG. However, in the embodiment of the present invention, the occurrence of jumping was suppressed up to a discharge voltage of 34 kV, and the effects of the present invention were fully recognized.

[0020]

[Effects of the Invention] As described above, by embedding the electrode in the side periphery of the insulator leg length, the electric field strength generated between the center electrode and the metal shell can be alleviated, so that jumping can be prevented. At the same time, the charged carbon generated during low-temperature combustion adheres to the tip of the long leg of the insulator.
It has the excellent effect of improving smoldering and staining resistance since it can suppress the accumulation.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a spark plug for an internal combustion engine, which is an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the main part thereof.

FIG. 3 is a perspective view of an insulator tip in another embodiment of the invention.

FIG. 4 is a comparison result of the discharge voltage at the time of occurrence of jumping with a conventional example.

[Explanation of symbols]

1 Spark plug for internal combustion engine 2 Insulator 3 Shaft hole 4 Center electrode 5 Resistor 6 Terminal electrode 7 Main metal fittings 8 Threaded part 9 Outer electrode 10 Recessed part 11 Electrode part 12 Lead part 13 Green sheet 14 Long leg part of insulator 15 Front end surface 16 Conductive glass seal 17 Wire packing

Claims (3)

[Claims] Claim 1: A concave portion is provided around the side circumference of the long leg portion of the insulator that holds the center electrode, and a paste-like ink containing 30 to 95 wt% of metal powder and 70 to 5 wt% of ceramic powder is injected into the concave portion. An electrode part is formed by printing or coating on an alumina green sheet in advance, and the printed or coated part is provided as the inner surface, and a lead part is configured to ensure electricity flow from this electrode part to the metal shell, and simultaneously fired. A spark plug for internal combustion engines that is tightly bonded. 2. A concave portion is provided around the side circumference of the long leg portion of the insulator that holds the center electrode, and a paste-like material is prepared in which 30 to 95 wt% of metal powder and 70 to 5 wt% of ceramic powder are mixed. An electrode part is formed by directly printing or coating the surface with ink, and a lead part is configured to ensure electricity supply from this electrode part to the metal shell, and the electrode part is covered with an alumina green sheet. A spark plug for an internal combustion engine, which is made by co-firing the two in close contact with each other. 3. The position of the recess provided around the long leg portion of the insulator is such that the distance A from the front end surface of the insulator is 2.0 mm or more,
The spark plug for an internal combustion engine according to claim 1 or 2, further comprising a depth T of the recessed portion of 0.1 mm or more.